Sleep sack



FIG. 1 is a front perspective view of a sleep sack;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof, the right side elevation being a mirror image thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a top plan view thereof shown in use.

The broken lines showing of an infant in FIG. 7 depicts environmental subject matter that forms no part of the claimed design. 

CLAIM The ornamental design for a sleep sack, as shown and described. 